FIG. 4 shows a conventional refrigerator (see Patent Document 1 for example). In FIG. 4, a reference number 1 represents a compressor, a reference number 2 represents an outdoor heat exchanger, a reference number 3 represents an indoor heat exchanger, a reference number 4 represents an accumulator and a reference number 5 represents a four-way valve, The outdoor heat exchanger 2 and the indoor heat exchanger 3 are connected to each other through a refrigerant passage 17. A refrigerant passage 17 is provided with the first expansion valve 11, the second expansion valve 12 and a third, expansion valve 13 in series.
The refrigerant passage 17 between the first expansion valve 11, and the second expansion valve 12 is provided with a receiver 7 for separating gas and liquid from each other. An inner heat exchanger 8 includes a high pressure-side heat transfer section 8a and a low pressure-side heat transfer section 8b. The refrigerant passage 17 between a second expansion valve 12 and a third expansion valve 13 is provided with the high pressure-side heat transfer section 8a of the inner heat exchanger 8. One end of the low pressure-side heat transfer section 8b of the inner heat exchanger 8 is connected to a refrigerant passage 14 and the other end of the low pressure-side heat transfer section 8b is connected to a refrigerant passage 15. The refrigerant passage 14 is an outlet-side pipe of the four-way valve 5, and the refrigerant passage 15 is an inlet-side pipe to the accumulator 4. A gas phase section of the receiver 7 is connected to a compressing chamber of the compressor 1 through a refrigerant passage 16 including a control valve 10. This conventional refrigerator uses carbon dioxide as a refrigerant.
A cooling operation of the refrigerator will be explained with reference to FIG. 5 which is a diagram showing “P(pressure)-h(enthalpy)”.
At the time of the cooling operation, CO2 refrigerant (gas refrigerant) discharged from the compressor 1 is introduced into the outdoor heat exchanger 2 through the four-way valve 5, and heat of the refrigerant is dissipated at a supercritical region (regions of points D to E in FIG. 5) in the outdoor heat exchanger 2. The CO2 refrigerant In a supercritical state flowing out from the outdoor heat exchanger 2 is primarily expanded in the first expansion valve 11 (regions of points E to F). and introduced into the receiver 7 in a gas-liquid two phases, and gas and liquid are separated here (points G and H).
A liquid refrigerant separated in the receiver 7 passes through the fully-opened second expansion valve 12 and flows into the high pressure-side heat transfer section 8a of the inner heat exchanger 8. While the liquid refrigerant flows from an inlet (point H) of the high pressure-side heat transfer section 8a toward an outlet (point I) of the high pressure-side heat transfer section 8a, the liquid refrigerant exchanges heat between itself and gas refrigerant which flows from an inlet (point K) of the low pressure-side heat transfer section 8b toward an outlet (point A) of the low pressure-side heat transfer section 8b. Then, the liquid refrigerant is secondarily expanded in the third expansion valve 13 (regions of points I to J). Thereafter, the liquid refrigerant is sent to the indoor heat exchanger 3 and is evaporated while it flows from an inlet (point J) of the indoor heat exchanger 3 to an outlet (point K) of the indoor heat exchanger 3 and becomes gas refrigerant. This gas refrigerant is again drawn into the compressor 1 and compressed. The drawing temperature is higher (i.e., temperature corresponding to point A) than the outlet temperature (temperature corresponding to point K) of the indoor heat exchanger 3 by a temperature (shown with “d”) increased by the internal heat exchange in the inner heat exchanger 8. The gas refrigerant separated by the receiver 7 is injected into the compressing chamber which is in a compression stroke of the compressor 1 through the refrigerant passage 16 (see point G).
The gas refrigerant is injected into the compressing chamber of the compressor 1 in this manner, and the gas refrigerant is mixed with a gas refrigerant in the compressing chamber, thereby facilitating the cooling effect and high density effect of the gas refrigerant in the compressing chamber. Therefore, the drawing temperature of the compressor 1 is increased by the internal heat exchange, and a temperature of the gas refrigerant in the compressing chamber is once reduced to a temperature corresponding to point C from a temperature corresponding to point B at the time of gas injection irrespective of a fact that the compression is started from this high drawing temperature, and the reduced temperature is again increased and the temperature corresponding to point D becomes a discharging temperature. Therefore, since the discharging temperature is affected by temperature reduction associated with the gas Injection, and the discharging temperature can be lower than a temperature (temperature corresponding to point D0) when the gas injection is not carried out and the refrigerant is compressed from point A to point D0, and the reliability of the compressor 1 can be enhanced.
[Patent Document 1]
Japanese Patent Application Laid-open No. 2001-296067 (page 8, FIGS. 4 and 5)
According to this conventional refrigerator, when a compression ratio of the compressor 1, i.e., a ratio of a discharging pressure at point D and a drawing pressure at point A shown in FIG. 5 is great at the time of warming operation for example when an outside temperature is low, the discharging temperature becomes abnormally high due to characteristics of the carbon dioxide which is a refrigerant. For this reason, even if a gas refrigerant separated by the receiver 7 is injected into the compressor 1, the discharging temperature is not lowered sufficiently and the reliability of the compressor 1 is not sufficient.
To avoid this situation, if the control valve 10 is further opened to:increase the amount of injection flow of the refrigerant, a liquid refrigerant separated in the receiver 7 is also injected. Therefore, the liquid refrigerant flows into the compressing chamber which is in the compression stroke of the compressor 1, and the incompressible liquid refrigerant is compressed. Thus, a cylinder, a bearing and the like which form the compressing chamber are worn, and reliability thereof can not be secured.